1. The Field of the Invention
This invention pertains to implantable catheters, and, more particularly, to systems for effecting the stabilization on the skin of a patient of the extracorporeal portion of an implanted vascular access catheter.
2. Background Art
It is now common to use an implanted catheter to repeatedly access the vascular system of a patient and with the catheter perform repeated therapeutic medical activity. Such therapeutic activity could include the intermittent or continuous infusion of medication and fluids, the periodic sampling of blood, or the continuous withdrawal and return of blood for processing outside of the body of the patient. The catheters used in these activities are referred to as vascular access catheters.
Before any therapeutic activity can actually commence, however, the vascular access catheter must be implanted in the body of the patient with the distal tip of the catheter residing at the location in the vascular system at which an intended therapeutic activity is appropriate. Typically, most of the length of an implanted vascular access catheter resides within blood vessels of the vascular system, extending from the distal tip of the catheter to a location in the vascular system at which the catheter, by traversing a puncture or incision formed through a wall of the blood vessel in which the catheter is disposed, enters into the surrounding subcutaneous tissue of the patient. The location at which this occurs is referred to as a venipuncture site. Venipuncture sites are classified on the basis of the position of a venipuncture site in relation to the center of the body of the patient. Central venipuncture sites are those at the superior or inferior vena cava. Midlavicular venipuncture sites are located medial of the shoulder of the patient, but lateral of the subclavian vein. Midline venipuncture sites enter the upper basilic or cephalic veins. The freedom to select among venipuncture sites is most curtailed relative to patients of slight stature, particularly small children and infants.
Proximal of the venipuncture site, the implanted catheter extends through the subcutaneous tissue of the patient to emerge through the skin at a location that is referred to as the skin exit site. Most skin exit sites are chosen as being locations at which the proximal end of the implanted catheter can be easily manipulated by medical personnel. Favored among such locations are the neck, the region about the collar bone, the upper leg, the upper arm, and the forearm.
Occasionally, the skin exit site is somewhat removed from the venipuncture site. Then a significant portion of the length of the implanted catheter must be embedded in the subcutaneous tissue of the patient in a surgically created tunnel that extends from the venipuncture site to the skin exit site. The disposition of a significant portion of the length of an implanted catheter in such a subcutaneous tunnel assists in stabilizing the implanted catheter by resisting sliding movement of the catheter back and forth, internally at the venipuncture site or externally at the skin exit site.
On the other hand, with patients of slight stature and particularly with small children and infants, the skin exit site is frequently located immediately adjacent to the venipuncture site. Under such conditions, the portion of the implanted catheter disposed in subcutaneous tissue is so short as to permit the body of the catheter to slide back and forth across the venipuncture site, as well as in and out of the skin exit site.
The portion of an implanted catheter that resides in a blood vessel of the vascular access system or within subcutaneous tissue is referred to as the implanted portion of that catheter. In all instances, a portion of the proximal end of an implanted catheter must remain outside of the body of the patient. It is this portion of an implanted catheter, from the proximal end thereof to the skin access site, that is referred to as the extracorporeal portion of the implanted catheter.
The extracorporeal portion of an implanted catheter must be capable of being selectively coupled to and uncoupled from the tubing and medical equipment outside the body of the patient that are required for therapeutic activity. Accordingly, the proximal end of virtually all vascular access catheters terminates in a catheter coupling hub that can be secured in fluid communication with such tubing and medical equipment, or can be capped, valved, or clamped closed between periods of actual use.
The repeated manipulation of the extracorporeal portion of an implanted catheter causes wear in the material of the catheter and reduces the reliability of the attachment between the proximal end of the catheter and the catheter coupling hub. In the absence of countermeasures, forces imposed on the extracorporeal portion of an implanted catheter result in motions of the extracorporeal portion of the catheter that cause damage to the catheter. Motion of the extracorporeal portion of an implanted catheter is also communicated to the skin access site, causing various complications depending upon the length of any subcutaneous tunnel in which a portion of the catheter is imbedded. Where such a subcutaneous tunnel is lengthy, motions of the extracorporeal portion of a catheter are relayed directly to the tissue along the subcutaneous tunnel, causing pain and irritation, precluding healing, and leading to infection. These results in turn can necessitate the explanation of the catheter. Where the portion of an implanted catheter extending subcutaneously between the venipuncture site and the skin exit site is short, motions of the extracorporeal portion of the catheter tend to slide the catheter in and out of the vascular system, causing bleeding and likewise leading to infection.
To counteract these undesirable consequences, a variety of measures are undertaken to stabilize the extracorporeal portion of an implanted catheter on the skin of the patient. Tie-down materials, such as bandaging, patches with upstanding anchoring posts, medical adhesive tape, belts, elastic bands, and sutures, are used for this purpose.
To enhance the effectiveness of such tie-down materials, otherwise unnecessary structures are formed on or attached to the catheter coupling hub or the portion of the proximal end of the catheter attached thereto. For example, it is common in the art of catheter implantation to provide one or more flap-like structures that extend laterally from the catheter coupling hub, from the portion of the proximal end of the catheter attached thereto, or from a tubular sleeve that is disposed about either or both of the catheter and the catheter coupling hub. These structures are referred to as stabilization wings.
Even without the assistance of any tie-down materials, a stabilization wing prevents a catheter coupling hub from rolling along the skin of the patient, pivoting about the skin exit site, and twisting the extracorporeal portion of the catheter between the skin exit site and the coupling hub. Sliding motions of a coupling hub on the skin of the patient in directions normal to the length of the catheter are curtailed by the use of tie-down materials applied over or about the coupling hub and against the skin. Tie-down materials also prevent movement of the coupling hub and associated catheter in directions aligned with the length of the catheter, motions that could dislodge the catheter from the skin exit site entirely. Stabilization wings enhance the purchase afforded on the catheter coupling hub by tie-down materials.
A system for coupling an implanted catheter to extracorporeal medical equipment and simultaneously stabilizing the extracorporeal portion of that catheter is complex to design. It is a process that must accommodate a variety of functional needs in an environment involving materials as different as human tissue, bodily fluids, flexible fluid conduits, rigid coupling structures, and various tie-down materials. The extracorporeal portion of an implanted catheter functions as an interface between the environment within the body of the patient at the distal tip of the catheter and extracorporeal medical equipment. At this interface, the patency of tubing, the minimizing of wear, the suppression of exit site infection, the freedom of access by medical personnel, and the inconspicuousness of the extracorporeal portion of the implanted catheter are each desired to be maintained to optimum degrees.
As new classes of materials are developed that are suitable for medical use, the potential of each in relation to existing catheter coupling and stabilization systems is investigated, and the design of such systems evolves accordingly.
Nonetheless, a significant problem in the design of coupling and stabilization systems arises from the contradictory material properties considered desirable among the various components of such systems.
The criteria of suitability for the implanted portion of a catheter that is disposed in the vascular system or the subcutaneous tissue of a patient are dramatically different from the criteria of suitability for the environment outside the body in which the extracorporeal portion of an implanted catheter is disposed and utilized. The implanted portion of a vascular access catheter must be so flexible and soft as to avoid damaging internal tissues and to minimize injury to the cells of the blood. The extracorporeal portion of that same implanted catheter must, by contrast, sustain repeated manipulation and predictable accidental or intentional abuse.
Among the extracorporeal portion of an implantable catheter assembly are components that are hard and entirely inflexible, such as clamps and coupling fixtures that must interact with extracorporeal tubing and medical equipment. In view of the possibility of extended contact by the extracorporeal portion of an implanted catheter with the skin of the patient, contrasting material properties of softness and flexibility suitable for skin contacting applications are also desirable in the extracorporeal interface.
Thus, many desirable material properties are inconsistent with others. As a result, efforts to optimize coupling and stabilization system designs have on occasion used differing classes of materials in various distinct components of the catheter coupling and stabilization system. The tension between the mechanical properties required in the extracorporeal interface for an implanted catheter and the patient comfort properties desirable therein has been resolved only to varying degrees in different systems.
One approach to achieving a marriage of the inconsistent material properties desired in a coupling and stabilization system has been to resort to nonunitary coupling and stabilization systems. Such systems involve some components that embody one set of desired material properties that are assembled in the field by medical personnel with other components that embody a contrasting set of desired material properties. For example, brackets optimizing patient comfort properties are secured to the skin of a patient and used as retainers to stabilize catheter coupling hubs made of tough materials possessed of optimized mechanical properties.
Coupling and stabilization systems configured from components assembled in the field are disadvantaged, however. Individual components can become lost, mismatched components can inadvertently be used together, or important components may never be employed as a result of slipshod practices. Individual components are small and difficult to manipulate, while the maintenance of inventories of a variety of individual interconnecting coupling and stabilization system elements increases institutional overhead.
The selection of structural elements for the extracorporeal interface and the relative positioning of the selected structural elements in a given coupling and stabilization system similarly require design trade-offs that are unlikely to be optimized in any single system.
For example, coupling and stabilization systems that utilize stabilization wings positioned at or adjacent to the catheter coupling hub of the system are effective in precluding movement of the catheter coupling hub. This high level of stability in the catheter coupling hub is obtained, however, at the cost of restricting the ease with which the catheter coupling hub can be manipulated by medical personnel. When stabilization wings in an extracorporeal interface are positioned longitudinally at or close to a catheter coupling hub, the stabilization wings and the catheter coupling hub share relatively similar degrees of freedom. As a consequence, the coupling and uncoupling of extracorporeal tubing and medical devices at the catheter coupling hub are undesirably difficult. Forces imposed on the catheter coupling hub or on the portion of the proximal end of the catheter attached thereto, and motions imparted to either as a result, are communicated directly to the stabilization wings, tending to dislodge the stabilization wings from the skin of the patient. This can be uncomfortable and may lead to tissue irritation at that location. Dislodgment of stabilization wings or a coupling hub from associated tie-down materials or from the skin is likely to lead to catheter damage or catheter explanation.
The positioning of stabilization wings along the proximal end of a catheter distally from the catheter coupling hub produces a different mix of consequences.
Stabilization wings have been longitudinally fixed on the exterior of the extracorporeal portion of a catheter tube at a distance from the catheter coupling hub. When secured to the skin of a patient, the stabilization wings of such systems permit easy access to and use of the catheter coupling hub, because of the flexibility embodied in the material of the catheter between the stabilization wings and the catheter coupling hub. Nonetheless, tortional and axial forces imposed on the catheter coupling hub are still communicated directly to the stabilization wings, as surely as if those stabilization wings were positioned immediately at the catheter coupling hub.
In some coupling and stabilization systems, stabilization wings are attached to the distal end of an elongated sleeve that is in turn secured at the proximal end thereof to the exterior of the catheter coupling hub. The full length of the interior of the sleeve is bonded to the exterior of the catheter tube distal of and adjacent to the coupling hub, producing a composite structure distal of the coupling hub. Such sleeves thicken, and therefore strengthen, the portion of the catheter tube enclosed therein, increasing the durability of the composite structure. Nonetheless, the composite structure tends to exhibit reduced flexibility, impairing intended movements of the catheter coupling hub relative to the stabilization wings. Also, axial forces imposed on the catheter coupling hub are communicated directly to the stabilization wings.
Some of these difficulties may be overcome, but not without foregoing other advantages.
Stabilization wings are, on occasion carried on a sleeve that can be slid along the extracorporeal portion of an implanted catheter and positioned on the skin of the patient at any desired distance from the catheter coupling hub. The securement of such stabilization wings to the skin prevents lateral movement of the portion of the catheter that is between the stabilization wings and the skin exit site. As the sleeve carrying the stabilization wings is not secured in any fixed relation to the catheter or the coupling hub, undesirable longitudinal and rotational movement of the catheter coupling hub relative to the stabilization wings is nonetheless common. Stabilization wings carried on slidable sleeves are susceptible to disposition at improper locations and are thus sensitive to, and in some cases limited in utility by, the skill and talent of specific medical personnel. Slidable sleeves may be overlooked and never used. Some are simply severed from the catheter assembly out of a misplaced desire to simplify the extracorporeal portion of the implanted structure. Longitudinally positionable sleeves carrying stabilization wings are known that completely succumb to this impulse by being manufactured with an axial slit through the sleeve. The sleeve may then be detached at will from the system of which it is supposed to be a component.
It may be realistic in addressing the diverse demands placed on the extracorporeal interface of an implanted catheter to acknowledge that any distinct coupling and stabilization system is advantageous in selected respects and disadvantaged in others.